With increasing needs to wirelessly identify and capture data related to physical objects, there has been an increased use of radio-frequency identification (RFID) and barcode technologies. RFID technologies offer the promise of non-line-of-sight identification, reading of many objects simultaneously with a single reader and the promise of supporting greater functionality including sensor inputs and large amounts of rewritable memory. For these reasons RFID has emerged as a preferred automatic identification and data capture technology.
RFID readers or interrogators are used for communicating with and powering tags affixed to objects. A unique ID code stored in the tag is communicated to the reader and associated with information in a database. At minimum an RFID tag consists of an electric circuit attached to an antenna on some substrate. The electronic circuit may be chipless. containing only passive elements (e.g. inductors. capacitors. resistors. diodes). or may contain an integrated circuit containing active electronic devices such as transistors. A reader consists of an RF transceiver unit attached to one or more antennas.
At lower operating frequencies (such as 125 KHz or 13.56 MHz) where the wavelength of the electromagnetic field is large compared to the operating distance, the coupling between the reader and the tag is often described as “near-field” coupling. In this case, the reader antenna and the tag antennas are coupled together either inductively with coils or capacitively with planar electrodes, in which the tag atenna can be resonant or non-resonant.
At higher operating frequencies (such as 915 MHz or 2.45 GHz) where the wavelength of the electromagnetic field is small compared to the operating distance (generally 1 meter or more), the interaction between the reader and the tag is known as “far-field.” In this case, the tag communicates information to the reader by reflecting or scattering back some of the electromagnetic field that is incident on the tag. The amount of power that the tag is able to scatter back to the reader is dependent on the antenna shape, size, and tuning, and is generally described by a normalized parameter known as the scattering cross section.
The form of electromagnetic communication between a tag and a reader is important, since it influences the shape and form of the tag and reader antennas. Capacitively coupled antennas may be untuned or tuned and require two electrically disconnected electrodes (see e.g. U.S. Pat. No. 6,611,199). Inductively coupled antennas generally require tuned antennas in the form of a coil. Far-field antennas can employ either one or two electrodes, but also require tuning as well, in order to maximize the scattering cross-section.
RFID tags of all forms present unique challenges to integration with products both electromagnetically and mechanically. Because RFID tags communicate with RFID readers via electromagnetic fields and waves, the product packaging materials and contents can strongly affect communications between reader and tag. Liquid and metallic materials are known to both absorb and reflect electromagnetic energy.
The physical integration of RFID tags with product packaging is generally challenging because many production processes have been well established and are unforgiving to significant changes or additions. Thus, there exists a need for innovative manufacturing methods as well as antenna designs to better integrate RFID tags into existing packaging materials and existing manufacturing methods at a low cost.
In the pharmaceutical industry, blister packages have emerged as a preferred method of packaging items for such reasons as security, product protection, display aesthetics, child-resistance, and medication compliance. Due to the increasing need to provide improved product tracking and tracing capabilities and additional security benefits there is a need to integrate RFID tags with blister packages.
Blister packages have been in use since at least the 1960s for packaging of a variety of products, including items such as toys, tools, chewing gum, and medication. A large body of prior art exists which cover various blister package designs and packaging materials (see e.g. U.S. Pat. Nos. 3,054,502, 2,503,493, 3,380,578, and 5,954,204).
Due to the existence of electrically conductive lidding film as a key component of the package, however, blister packages present unique challenges to integration of RFID tags. The lidding film typically consists of thin metal foil (0.6-1 mil=10 to 25 microns) and may incorporate additional laminated layers, such as paper or PET, and other coatings, for purposes such as heat sealing and printing. If RFID tag labels are applied to the lidding film, the electrical conductivity of the lidding film can detune RFID tag antennas and reflect electromagnetic fields and waves preventing necessary power transfer and communications—ultimately leading to poor RFID performance.
One solution to this problem is to add spacing or ferrite materials between the RFID tag and the blister package lidding film; however, this can add significant cost to overall package materials and production, while providing only a minor improvement in RFID performance.
Additionally, because the lidding film is designed to seal the contents in the package and act as a protective barrier, simply replacing the lidding film with any RFID tag label is not a viable option. The tag antenna must be designed so that the protective barrier is not compromised. Although various non-metallic non-conductive films have been developed as an alternative to metal foil lidding materials, the metal foils remain the most attractive in terms of cost.
Since the blister seal must not be compromised and also since the surface area between adjacent blisters is limited, an additional challenge is to create an RFID antenna that will fit within the limited available area in between adjacent blisters.
In the case of the tuned coil antenna employed for inductive coupling, it is desirable to maximize the enclosed area of the coil as well as the number of turns in order to maximize the mutual inductance between the tag and reader and also achieve the proper inductance value to enable resonant tuning. In addition, since the thickness of the blister pack foil lidding is generally 30 microns or less, it is necessary to maintain the width of the metal coil traces to a few hundred microns or greater in order to prevent excessive resistive loss in the tag antenna coil. As a result of all these factors, it is a great challenge to create an antenna that will fit within the limited surface area of the blister pack and also avoid cutting the portions of the foil which seal the blisters.
Although there have been several attempts to integrate blister packaging with RFID functionality, these prior inventions rely on antennas and electronic devices that are external to the blister package, and are not an integral part of the blister pack materials themselves. U.S. Pat. No. 6,244,462, for example, describes an external paper box or sleeve, with conductive traces, monitoring circuit, and transceiver into which a conventional blister package is inserted. Other prior art is specifically intended for monitoring the dispensing of medication in unit-dose blister packages, incorporate conductive traces located above the enclosed contents, which when broken, provide an indication that the contents have been removed. U.S. Pat. No. 6,574,166, for example, describes a package for monitoring medication compliance, where the conductive traces for sensing are integrated within the blister package, but the monitoring circuit and transceiver with antenna are located either external to the package or added as extra components to the package itself. The use of external devices or high-conductivity printed layers adds undesirable cost and complexity to the process of blister pack manufacture.
In order to achieve low-cost and large-scale manufacture of blister packages with RFID functionality, there still exists a need for innovative package designs and manufacturing methods which can enable better integration of an RFID circuit and antenna with the existing materials and processes used in blister pack manufacture.